VProbes attempts to provide a set of tools for answering the question, "What the heck is this computer doing?" It's an open-ended question, so vprobes is accordingly open-ended, as well. In its current form, it provides an interactive, safe way of instrumenting a running VM at any level: from user-level processes down to the kernel, and even into VMware's VMM and hypervisor, if need be.
First, we are aiming to provide a Dtrace-like tool for other commercially important operating systems than Solaris. Second, VProbes can combine with other virtualization-based techniques in powerful ways. For example, VProbes and deterministic replay combine to make the most potent tool that I'm aware of for debugging intermittent performance anomalies.
Links to other Cheap or Free Mac Software: